The invention is based on a surge arrester having a cylindrically symmetrical housing which can be grounded, through which a plug connection is passed which can be brought to a high-voltage potential, and having an active part which is arranged in the housing and is aligned along the axis of symmetry and has two connection fittings, having at least one varistor element arranged between the two connection fittings, and having a tensioning apparatus which acts on the connection fittings and the at least one varistor element to form a contact force, in which surge arrester the active part is surrounded by an elastic dielectric sleeve which ensures the insulation from the housing.
An arrester of the abovementioned type is offered by numerous manufacturers commercially and is used for the protection of metal-encapsulated, gas-insulated switchgear assemblies. The arrester is in this case connected to a system plug contact which carries high voltage and has an outer or inner cone, and then limits overvoltages which are produced by switching processes or by reflection of traveling waves. The arrester contains a housing which is kept at ground potential and is protected against direct contact, and an active part which is installed in the housing and is formed from varistor elements, particularly based on metal oxide, without any spark gaps. The active part is encased in a dielectric composed of silicone rubber, whose outer surface at least partially rests on the inner surface of the housing. Such an arrester generally has semiconductive or conductive field-control elements to control the electric field between the active part, which is at high-voltage potential, and the housing, which is kept at ground potential.
EP 0 810 613 A2 describes a surge arrester having an active part embedded in a cast housing composed of dielectric material. Two connection fittings and varistor elements of the active part are braced with respect to one another by means of a loop composed of dielectric material, forming a contact force.
In the surge arrester according to the invention, the active part is held together and has contact force applied to it by at least one loop which is mounted on its two connection fittings. This gives the active part high mechanical strength in a manner which is simple in production engineering terms and is thus cost-effective. At the same time, a housing which surrounds the active part is in the form of a bottle, and this housing has a housing section in the form of a bottle neck, in which an electrical conductor is routed which is connected to one of the two connection fittings, is electrically conductively connected to the plug connection, and is cylindrically symmetrical. This results in an electric field being formed in the interior of the housing which makes it unnecessary to have any field-controlling, semiconductive or conductive elements and coatings between the active part and the wall of the housing even if the active part is not cylindrically symmetrical as a result of the holding loop. At the same time, the surge arrester is distinguished by excellent long-term stability owing to the mechanically very strong active part and owing to the lack of any field-controlling elements.
A particularly homogeneous distribution of the electric field, and thus a particularly advantageous dielectric response of the surge arrester, are achieved if there is a conically expanding housing section adjacent to the housing section in the form of a bottle neck, in which expanding housing section an end (which is connected to one of the two connection fittings) of the electrical conductor, which is connected to the plug connection, is routed.
It is advantageous for the housing section which is in the form of a bottle neck to expand at its end facing the plug connection, since the expansion then acts as a stop for mounting elements which are guided on this housing section. Such mounting elements are advantageously a mounting flange guided on the housing section in the form of a bottle, and a compression spring arranged between the mounting flange and the expanded area.
Since increased pressures may possibly occur when any possible overloading of the surge arrester occurs, the housing, which is in the form of a bottle, is generally designed to be pressure-resistant and is provided with an overpressure valve. This overpressure valve can advantageously be arranged on the housing base or may be the base itself, provided with a weak point. When the overpressure valve responds, hot gases emerging from the housing in the form of a bottle can then be removed without any problemsxe2x80x94and without the plug connection being damaged.
Dielectrically undesirable gaps and/or pores between the suppressor active part and a dielectric sleeve provided between the active part and the housing are avoided by coating the active part with an adhesion promoter. Pores and/or gaps which nevertheless occur in the housing interior between the active part and the housing wall are filled with a gel-like dielectric in order to improve dielectric strength.